What's Going On...

Kassandra • 23 & living with my best friend/soul mate. Fur mama to a German Sherpherd & Siamese Kitty. I own an online boutique, check it out :) *under construction*
My last AF ends Jan. 23 and I haven't had it again since. I've been BD'ing and have tested 6 times since and still no sign of being pregnant. 
I don't have any odd symptoms besides my appetite slighty shrinking, I have lost 2 lbs and occasional nausea.
Any know what could be going on ? :/ I've already missed my March AF so waiting on my April...?